| /******************************************************************************* |
| * Copyright (c) 2007, 2010 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| * EclipseSource - ongoing development |
| *******************************************************************************/ |
| package org.eclipse.equinox.p2.query; |
| |
| import java.lang.reflect.Array; |
| import java.util.*; |
| import org.eclipse.core.runtime.IProgressMonitor; |
| import org.eclipse.core.runtime.NullProgressMonitor; |
| import org.eclipse.equinox.internal.p2.metadata.Messages; |
| |
| /** |
| * A collector is a generic visitor that collects objects passed to it, |
| * and can then express the result of the visit in various forms. The collector |
| * can also short-circuit a traversal by returning <code>false</code> from |
| * its {@link #accept(Object)} method. |
| * <p> |
| * This default collector just accepts all objects passed to it. Clients may subclass |
| * to perform different processing on the objects passed to it. |
| * @param <T> The type of object accepted by this collector |
| * @since 2.0 |
| */ |
| public class Collector<T> implements IQueryResult<T> { |
| private Set<T> collected = null; |
| |
| public static final Collector<?> EMPTY_COLLECTOR = new Collector<Object>() { |
| public boolean accept(Object val) { |
| return false; |
| } |
| }; |
| |
| @SuppressWarnings("unchecked") |
| public static final <T> Collector<T> emptyCollector() { |
| return (Collector<T>) EMPTY_COLLECTOR; |
| } |
| |
| /** |
| * Creates a new collector. |
| */ |
| public Collector() { |
| super(); |
| } |
| |
| /** |
| * Accepts an object. |
| * <p> |
| * This default implementation adds the objects to a list. Clients may |
| * override this method to perform additional filtering, add different objects |
| * to the list, short-circuit the traversal, or process the objects directly without |
| * collecting them. |
| * |
| * @param object the object to collect or visit |
| * @return <code>true</code> if the traversal should continue, |
| * or <code>false</code> to indicate the traversal should stop. |
| */ |
| public boolean accept(T object) { |
| getCollection().add(object); |
| return true; |
| } |
| |
| /** |
| * Adds the elements from one collector to this collector |
| * @param queryResult The collector from which the elements should be retrieved |
| */ |
| public void addAll(IQueryResult<T> queryResult) { |
| boolean keepGoing = true; |
| for (Iterator<T> iter = queryResult.iterator(); iter.hasNext() && keepGoing;) { |
| keepGoing = accept(iter.next()); |
| } |
| } |
| |
| /** |
| * Returns the collection that is being used to collect results. Unlike {@linkplain #toSet()}, |
| * this returns the actual modifiable collection that is being used to store results. The |
| * return value is only intended to be used within subclasses and should not be exposed |
| * outside of a collection class. |
| * |
| * @return the collection being used to collect results. |
| */ |
| protected Collection<T> getCollection() { |
| if (collected == null) |
| collected = new HashSet<T>(); |
| return collected; |
| } |
| |
| /** |
| * Returns whether this collector is empty. |
| * @return <code>true</code> if this collector has accepted any results, |
| * and <code>false</code> otherwise. |
| */ |
| public boolean isEmpty() { |
| return collected == null || collected.isEmpty(); |
| } |
| |
| /** |
| * Returns an iterator on the collected objects. |
| * |
| * @return an iterator of the collected objects. |
| */ |
| public Iterator<T> iterator() { |
| return collected == null ? Collections.<T> emptyList().iterator() : collected.iterator(); |
| } |
| |
| /** |
| * Returns the number of collected objects. |
| */ |
| public int size() { |
| return collected == null ? 0 : collected.size(); |
| } |
| |
| /** |
| * Returns the collected objects as an array |
| * |
| * @param clazz The type of array to return |
| * @return The array of results |
| * @throws ArrayStoreException the runtime type of the specified array is |
| * not a super-type of the runtime type of every collected object |
| */ |
| public T[] toArray(Class<T> clazz) { |
| int size = collected == null ? 0 : collected.size(); |
| @SuppressWarnings("unchecked") |
| T[] result = (T[]) Array.newInstance(clazz, size); |
| if (size != 0) |
| collected.toArray(result); |
| return result; |
| } |
| |
| /** |
| * Returns a copy of the collected objects. |
| * |
| * @return An unmodifiable collection of the collected objects |
| */ |
| public Set<T> toSet() { |
| return collected == null ? new HashSet<T>() : new HashSet<T>(collected); |
| } |
| |
| /** |
| * Performs a query on this results of this collector. |
| */ |
| public IQueryResult<T> query(IQuery<T> query, IProgressMonitor monitor) { |
| IQueryResult<T> result; |
| if (monitor == null) |
| monitor = new NullProgressMonitor(); |
| try { |
| monitor.beginTask(Messages.performing_subquery, 1); |
| result = query.perform(iterator()); |
| monitor.worked(1); |
| } finally { |
| monitor.done(); |
| } |
| return result; |
| } |
| |
| /** |
| * Returns the collected objects as an immutable collection. |
| * |
| * @return An unmodifiable collection of the collected objects |
| */ |
| public Set<T> toUnmodifiableSet() { |
| if (collected == null) { |
| return Collections.emptySet(); |
| } |
| return Collections.unmodifiableSet(collected); |
| } |
| } |